1. Field of the Invention
The present invention relates generally to an intercooler for a supercharged internal combustion engine and more specifically to an intercooler which is integrated with the engine cooling system and wherein the coolant in both the engine cooling system and the intercooler, is permitted to boil (viz., absorb its latent heat of vaporization) and the vapor used as a vehicle for removing heat from both arrangements.
2. Description of the Prior Art
In order to improve engine performance superchargers especially exhaust gas driven turbochargers are often fitted to internal combustion engines. However, these devices while improving engine performance have encountered drawbacks in that the temperature of the air charged into the cylinders increases due to compression (often as high as 150.degree.-170.degree. C.) which reduces the density of the air thus reducing charging efficiency, and tends to induce knocking (in Otto cycle engines).
To solve the latter mentioned problem it is common to retard the ignition timing and/or lower the compression ratio. However, this tends to reduce engine power output. Accordingly, it has been proposed to interpose an intercooler between the supercharging compressor and the engine cylinders in order to reduce the temperature of the inducted charge.
FIG. 1 of the drawings shows a first example of a previously proposed intercooler arrangement. This arrangement (disclosed in the Japanese publication "Jidosha Kogaku"--Vol. 32 No. 9 pages 86-88 published in September 1983) employs an air-cooled heat exchanger 101 which is disposed as shown, at the forward end of the vehicle 102 so as to be exposed to an adequate flow of air and at some distance from the engine per se. However, such an arrangement while not excessively increasing the crowding of the engine room or compartment and simultaneously being exposed to a strong natural draft during forward movement of the vehicle, suffers from the drawback that excessively long conduits 104, 106 are required to conduct the air from the compressor of the turbocharger 108 to the heat exchanger 101 and back again to the induction manifold 110 of the engine. These long conduits 104, 106 of course produce a flow restriction which reduces charging efficiency and complicate the layout of the forward end of the engine compartment.
FIG. 2 shows a second prior art intercooler arrangement wherein, in order to obviate the need for long relatively large diameter air conduits such as used in the arrangement disclosed hereinabove, a water cooled heat exchanger 201 is employed. However, this arrangement has suffered from the drawbacks of being heavy (due to the use of a relatively large amount of liquid coolant used therein) and from the need to use a coolant circulation pump 202 to move the heated liquid coolant (usually water or a mixture of water and anti-freeze) from the heat exchanger 201 to a cooling radiator 204 and back again. In the illustrated arrangement, the operation of the coolant circulation pump 202 is controlled in response to a temperature responsive valve arrangement 206 disposed in the heat exchanger 201. However, despite this control measure, the parasitic pump 202 consumes an undesirable amount of engine power.
Japanese Patent application first provisional publication No. 56-146417 discloses an arrangement wherein in order to eliminate the need for an additional cost and weight increasing radiator, such as #204 used in the arrangement shown in FIG. 2, a system wherein the engine radiator is used to cool the coolant circulated through the liquid cooled heat exchanger as well as that circulated through the engine coolant jacket. However, with this arangement the coolant circulated to the heat exchanger is hotter than in the case wherein an individual radiator is used, and thus reduces the effectiveness of the intercooler. Viz., with this arrangement as the liquid coolant within the engine cooling system is controlled to approximately 70.degree.-80.degree. C. (by way of example) the temperature difference between the inlet and exhaust ports of the intercooler heat exchanger is small (for example 4.degree. C.) and therefore a large amount of coolant must be circulated therethrough to achieve the desired cooling effect. This of course increases the amount of power consumed by the intercooler coolant circulation pump.
It should be also noted that as the difference between the temperature of the air immediately upstream and that immediately downstream of the aircooled type intercooler is also relatively small efficient heat exchange is severdy inhibited.
FIG. 3 shows another type of previously proposed intercooler arrangement. This arrangement is integrated with the cooling system of the associated engine. In this arrangement coolant from a reservoir 301 is fed to a heat exhanger 302 which forms a vital part of the intercooler 303 and to a pressure pump or compressor 304. The pressurized fluid discharged by the pump 304 is circulated through the engine coolant jacket 305 to absorb the heat produced by the engine. The resulting high pressure-temperature mixture of boiling coolant and vapor is ejected toward a condenser through a variable nozzle jet pump 307. Simultaneously, the liquid coolant fed into the intercooler heat exchanger 302 absorbs heat from the supercharged air passing through the intercooler 303 and vaporizes. This vapor is extracted from the heat exchanger and directed to the condenser 306 under the influence of the venturi action produced by the ejection of the high temperature-pressure liquid/vapor mixture ejected from the variable nozzle jet pump 307. The vaporized coolant is condensed in the condenser 306 and returned to the reservoir 301.
However, this arrangement has encountered several drawbacks in that the compressor 304 consumes valuable engine output, in that it is very difficult to control the temperatures in the system to desired levels with any degree of reliability and in that the liquid coolant fed to the intercooler heat exchanger sometimes becomes excessively heated forming a superheated vapor which lowers the heat exchange efficiency of the intercooler. Further, upon stopping the engine the condensation of the vaporized coolant in the system induces a sub-atmospheric pressure therein which tends to induct contaminating air into the system. The system once contaminated with air tends to lose its efficiency due to the insulating pockets and/bubbles of air which can absorb little or no heat and which are inevitably find their way into the condenser of the system. For further disclosure relating to this device, reference may be had to "MOTOR TREND" published in the U.S. in June 1983 and/or to Japanese Patent Application First Provisional Publication Sho No. 56-146417 (1981).
FIG. 4 shows yet another example of previously proposed intercooler (disclosed in Japanese Patent Application First Provisional Publication Sho No. 57-46016 laid open to public inspection on Mar. 16, 1982). In this arrangement liquid coolant from the engine radiator is admitted under the influence of gravity to a heat exchanging device 409 via a valve 410. This valve is controlled by a level sensor 411 in a manner to maintain an essentially constant level of liquid coolant within the device. The hot supercharged air from the turbo-charger compressor C, passes over and around a plurality of essentially vertically arranged pipes or conduits 412 containing liquid coolant. A vacuum pump or the like 413 driven by an electric motor 414 (or alternatively by way of a mechanical connection with the engine crankshaft) is used to reduce the pressure within the liquid filled portion of the heat exchanger 409 to a level whereat the coolant boils at a suitably low temperature. The coolant vapor extracted from the heat exchanger by the pump 413 is discharged into tthe conduit 415 leading from the engine coolant jacket 416 to the engine radiator 408 and permitted to mix with the liquid coolant and condense at essentially atmospheric pressure.
However, this arrangement has suffered from the drawbacks that the vacuum pump 413 is relatively large and bulky consuming valuable engine room space as well as engine power and in that temperature control with respect to engine operation (e.g. engine load) is not taken into consideration.